An impact-type air driven screw fastener, by whose driver the screw is put into to some degree and rotated to be fastened, can improve greatly the efficiency of screw fastening comparing with a motor driver which is activated by only rotation.
However, when a gypsum board is fixed to a C-type steel plate structural material which is molded from a steel plate of 0.5 mm or 0.8 mm thick and commonly named as `Keiten (Japanese)`, if a drilling screw for a steel plate is fastened by utilizing the impact-type air driven screw fastener, the following problems are caused; a screw fastened previously is loosened or buried into the gypsum board by the impact of hammering of the screw fastened next. Particularly, as shown in FIG. 4, when two sheets of gypsum board 2, 3 are set so as to butt against each other on the C-type steel plate structural material 1 and the screws 4, 5 are fastened to the gypsum boards 2, 3, respectively, the following problems are caused due to the small thickness of the C-type steel plate structural material 1; as shown in the same figure, deformation and vibration of the C-type steel plate structural material 1 are caused by the impact of hammering, thereby the screw 4 fastened previously may be buried into the gypsum board 2 and the coating paper 6 of the gypsum board 2 may be broken so that the load strength of the gypsum board 2 is decreased, alternately, as shown in FIG. 5, a thread crest 7 provided at the place, where the screw 4 fastened previously is fitted into the C-type steel plate structural material 1, may be deformed or damaged so that the fastening force may be decreased, resulting in loose of screw 4. Therefore, in order to fasten the gypsum board to the C-type steel plate structural material, a commonly used fastener is not the impact-type air driven screw fastener, but the motor driver which is activated with only rotation.
On the other hand, high efficiency has been required in fastening the gypsum board to the metal steel such as C-type steel plate structural material. The decrease of load strength and fastening power would be caused by deformation of the steel plate due to hammering of screws into the gypsum board and the C-type steel plate structural material. Accordingly, in order to improve efficiency in the fastening, screw fastening with the impact-type air driven screw fastener must be facilitated in the situation decrease of load strength and fastening power is eliminated. In such situation, there is a technical problem to be solved. The object of the present invention thereby is to solve this problem.